The present invention generally relates to fluid dispensing and more particularly, to an improved fluid dispensing system including a weight monitor.
Known fluid dispensing systems include a pump with an inlet connected to a supply of material and a discharge connected to a fluid dispenser. For precision dispensing, the dispenser normally includes a valve which permits fluid to pass through a discharge opening such as a spray nozzle or fluid tip. In some systems, the dispenser valve is operated by a program controlled device so that fluid is dispensed in precise or metered amounts.
In many applications it is often desirable that precise patterns, metered amounts or both be dispensed. Further, in order to optimize the use of the material being sprayed, it is desirable that a constant amount of material be deposited on the object of interest. For example, in precision dispensing systems used to apply a coating of material on surfaces of can bodies, the user normally specifies the amount of material to be deposited by its weight, for example, 160 milligrams (xe2x80x9cmgxe2x80x9d) of material per can. With known systems, given a desired weight and density of material to be deposited, the flowrate of material expected to be discharged from the nozzle can be determined from the size of the nozzle orifice and estimates of the nozzle pressure and the viscosity of the material. Given an expected flowrate, the time the dispensing nozzle is held open to dispense the desired weight of material can also be determined.
While such systems have proven to provide an acceptable performance, there is a continuing effort to improve the system""s performance. Can bodies are typically coated during the manufacturing process at rates of up to several hundred cans per minute. Further, any changes in the variables used to determine the expected flowrate, e.g., the coating material viscosity, will affect the flowrate of material through the nozzle and thus, the weight of material used to coat the can body. Such variations in the weight of the coating material used have a significant impact on manufacturing costs. For example, if the weight of the coating material is greater than a specified weight, more coating material than required is being used. When the value of that excess material is accumulated over thousands or millions of cans being coated, it adds up to a very significant cost. Obviously, there is a need to reduce the unnecessary cost of applying excess coating material to a can or other object. In the other extreme, if there is too little coating material used in the process, the result is improperly coated cans. An improperly coated can may have an adverse effect on the can""s ability to function for storage. In some cases, the can may suffer accelerated deterioration (i.e., shortened shelf life), and in others (e.g. for foods and beverages) the contents may be adversely affected (e.g., taste, spoilage). Improper coating, therefore, is undesirable and adds substantial expense because improperly coated cans must be rejected and disposed of, or reprocessed by inspecting, hand sorting, cleaning and recoating.
Thus, there is a need for an improved fluid dispensing system in which variations in the coating material being dispensed and applied can be automatically detected and addressed.
The present invention provides a fluid dispensing system with an improved monitoring of the quality of the fluid dispensing process. The fluid dispensing system of the present invention has a monitoring system providing an early indicator of a potential problem in a coating line, thereby providing a higher quality finished coated product. The fluid dispensing system of the present invention can be used to prevent first, the use of excessive coating material, thereby reducing manufacturing costs, and second, the use of too little coating material, thereby improving the quality of the finished coated product. Further, the present invention permits deviations in the fluid dispensing process to be corrected prior to a large number of faulty coatings occurring, thereby providing a more efficient and economical fluid coating line. Thus, the fluid dispensing system of the present invention is especially useful in coating line applications where a large number of objects are being coated over successive fluid dispensing cycles.
In accordance with the principles of the present invention and the described embodiments, a fluid dispensing system is provided for monitoring a weight of a fluid dispensed by a fluid dispenser. A first monitoring device determines a first flow characteristic of the pressurized fluid flowing through the fluid dispenser, and a second monitoring device determines a second flow characteristic of the pressurized fluid flowing through the fluid dispenser. A monitor control produces an output representing a weight of the fluid dispensed by the fluid dispenser as a function of the first and second flow characteristics.
In one aspect of the invention, the first and second monitoring devices are pressure and viscosity monitoring devices. Further, the fluid dispenser is operated over intervals of time; and the monitor control produces pressure and viscosity values of the pressurized fluid flowing through the fluid dispenser during an interval of time.
In a further aspect of the invention, the monitor control stores a value related to a size of an orifice in the fluid dispenser through which the pressurized fluid is dispensed; and the monitor control produces a volume value representing a volume of fluid flowing through the fluid dispenser during the interval of time as a function of the size of the orifice. The monitor control also stores a value related to a density of the pressurized fluid and produces the output representing the weight of fluid dispensed by the fluid dispenser during the interval of time as a function of the density value.
In another embodiment, the present invention includes a method of monitoring a weight of a fluid being dispensed by a fluid dispenser. In the method, a fluid dispenser executes a fluid dispensing cycle to apply a fluid coating to an object. First and second flow characteristics of the fluid dispensed by the fluid dispenser during the fluid dispensing cycle are then determined; and thereafter, a weight of the fluid dispensed by the fluid dispenser during the fluid dispensing cycle is determined as a function of the first and second flow characteristics.
In an aspect of this invention, the first and second flow characteristics are the pressure and viscosity of the fluid dispensed by the fluid dispenser during the fluid dispensing cycle.
Various additional advantages, objects and features of the invention will become more readily apparent to those of ordinary skill in the art upon consideration of the following detailed description of the presently described embodiments taken in conjunction with the accompanying drawings.